A

TRAINING REPORT

On

GLOBAL SYSTEM FOR MOBILE COMM.(GSM)

Submitted in the practical fulfillment for the award of Degree of Bachelor of Technology

in

ELECTRONICS & COMMUNICATION ENGINEERING

From

KURUKSHETRA UNIVERSITY, KURUKSHETRA

Submitted To:- Submitted By:-

Er.SHIV GOEL (H.O.D,ECE) NITIN MITTAL(2908224)

DEPARTMENT OF ELECTRONICS & COMMUNICATION ENGG.

KURUKSHETRA INSTITUTE OF TECHNOLOGY &

MANAGEMENT,KURUKSHETRA-1361191

TRAINING REPORT GSM

CONTENTS

Acknowledgement 3

Abstract 4

List of figures 5

Company Profile 6

INTRODUCTION to GSM 10

Generation of GSM 11

The GSM NETWORK 13

GSM Architechture 26

GSM Interfaces 27

Call Processing 29

GSM Handover 33

Conclusion 35

References 36

2

TRAINING REPORT GSM

ACKNOWLEDGEMENT

Many lives & destinies are destroyed due to the lack of proper guidance, directions &

opportunities.

With profound respect and gratitude, I take the opportunity to convey my thanks for permitting me

to complete my training in MTNL.

I would like to express a deep sense of gratitude and thanks to Mr. VIJENDER SINGH (Field

Trainer) without whose wise counsel and able guidance, it would have been impossible to

complete the report in this manner.

The help rendered by Mr. AJAY KUMAR BHALLA (Course In charge), is greatly

acknowledged.

Finally, I’m extremely grateful to all the technical staff of ITTM (Shadipur) and MTNL

Telephone Exchange’s at Karol Bagh and Shakti Nagar for their co-operation and guidance that

has helped me a lot during the course of training. I have learnt a lot working under them and I will

always be indebted to them for this value addition in me.

It was really a good experience working in a professionally managed firm and learning from such

good and knowledgeable people. I hope it will really help me in future.

.NITIN MITTAL

(Kurukshetra Institute of Technology & Management)

3

TRAINING REPORT GSM

ABSTRACT

Global System for Mobile communications (GSM: originally from Group Special Mobile) is the

most popular standard for mobile phones in the world. Its promoter, the GSM Association,

estimates that 82% of the global mobile market uses the standard GSM is used by over 2 billion

people across more than 212 countries and territories. Its ubiquity makes international roaming

very common between mobile phone operators, enabling subscribers to use their phones in many

parts of the world. GSM differs from its predecessors in that both signaling and speech channels

are digital call quality, and so is considered a second generation (2G) mobile phone system. This

has also meant that data communication were built into the system using the 3rd Generation

Partnership Project (3GPP)The GSM logo is used to identify compatible handsets and equipment

The key advantage of GSM systems to consumers has been better voice quality and low-cost

alternatives to making calls, such as the Short message service (SMS, also called "text

messaging"). The advantage for network operators has been the ease of deploying equipment from

any vendors that implement the standard. Like other cellular standards, GSM allows network

operators to offer roaming services so that subscribers can use their phones on GSM networks all

over the world. Newer versions of the standard were backward-compatible with the original GSM

phones. For example, Release ''97 of the standard added packet data capabilities, by means of

General Packet Radio Service (GPRS). Release ''99 introduced higher speed data transmission

using Enhanced Data Rates for GSM Evolution (EDGE). In addition to digital transmission, GSM

incorporates many advanced services and features, including ISDN compatibility and worldwide

roaming in other GSM networks. The advanced services and architecture of GSM have made it a

model for future third-generation cellular systems, such as UMTS. This paper will give an

overview of the services offered by GSM, the system architecture, the radio transmission structure,

and the signalling functional architecture.

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TRAINING REPORT GSM

LIST OF FIGURES

S.NO. FIGURE NO. DESCRIPTION PAGE NO.

1. 1.1 Generation Of GSM 8

2. 1.2 The Base Station Subsystem 13

3. 1.3 GSM BSS 13

4. 1.4 GSM BTS 15

5. 1.5 A Base Transceiver Station(BTS) Antenna In Paris 16

6. 1.6 Internal view of BTS 16

7. 1.7 2-G BTS 16

8. 1.8 3-G BTS 20

9. 1.9 Network Switching Subsystem 32

10. 2.0 GSM Architechture 33

11. 2.1 Call from Mobile to PSTN 42

12.. 2.2 Call from PSTN to Mobile 46

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TRAINING REPORT GSM

COMPANY PROFILE

MTNL was set up on 1st April, 1986 by the Government of India to upgrade the quality of

telecom services, expand the telecom network, introduce new services and to raise revenue for

telecom development needs of India's key metros . Delhi, the political capital and Mumbai, the

business capital of India. In the past 23 years, the company has taken rapid strides to emerge as

India's leading and one of Asia's largest telecom operating companies. Besides having a strong

financial base, MTNL has achieved a customer base of 8.06 million as on 31st March 2009.

The company has also been in the forefront of technology induction by converting 100% of its

telephone exchange network into the state-of-the-art digital mode.

The Govt. of India currently holds 56.25% stake in the company.

6

INSTITUTE OF TELECOM TECHNOLOGY AND MANAGEMENT (ITTM)

ITTM, a unit of MTNL Delhi, is an advanced level training center located at MTNL Sanchar

Bhawan, Shadipur, Delhi-110008. It has facilities and infrastructure suitable to impart training in

the latest technologies in telecom sectors along with management module. Certain points which

give extra weightage to ITTM are:

ITTM is conveniently located near Metro Station and reputed Shadipur Bus Terminal.

Huge space with modern air conditioned lecture rooms.

Ample parking space.

ITTM has OFC Lab, GSM Lab, IP Networking Lab, Broadband and Computer Labs to give first hand practical experience.

Qualified and Experienced Faculty to share their valuable field experience.

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Above all, MTNL, a brand which needs no introduction in telecom industry in India as well as abroad.

ITTM Delhi is conducting a number of technical and management courses for its employees to

enhance their knowledge, skills and attitude to perform in a better and professional way. Now,

management of MTNL has decided to contribute its services as a part of corporate social

responsibility to train Engineering students so that their knowledge and skill level may match best

in the industry. ITTM is going to start Summer Industrial Training for engineering students in the

month of April, May, June and July 2011. The details of the training programme are attached

herewith.

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History

Early European analogue cellular networks employed an uncoordinated mix of technologies and protocols that varied from country to country, preventing interoperability of subscriber equipment and increasing complexity for equipment manufacturers who had to contend with varying standards from a fragmented market. The work to develop a European standard for digital cellular voice telephony began in 1982 when the European Conference of Postal and Telecommunications Administrations (CEPT) created the Groupe Spécial Mobile committee and provided a permanent group of technical support personnel, based in Paris. In 1987, 15 representatives from 13 European countries signed a memorandum of understanding to develop and deploy a common cellular telephone system across Europe. The foresight of deciding to develop a continental standard paid off, eventually resulting in a unified, open, standard-based network larger than that in the United States.

France and Germany signed a joint development agreement in 1984 and were joined by Italy and the UK in 1986. In 1986 the European Commission proposed to reserve the 900 MHz spectrum band for GSM. By 1987, basic parameters of the GSM standard had been agreed upon and 15 representatives from 13 European nations signed a memorandum of understanding in Copenhagen, committing to deploy GSM. In 1989, the Groupe Spécial Mobile committee was transferred from CEPT to the European Telecommunications Standards Institute (ETSI)

Phase I of the GSM specifications were published in 1990. The historic world's first GSM call was made by the Finnish prime minister Harri Holkeri to Kaarina Suonio (mayor in city of Tampere) in July 1 1991. The first network was built by Telenokia and Siemens and operated by Radiolinja. 1992, the first short messaging service (SMS or "text message") message was sent and Vodafone UK and Telecom Finland signed the first international roaming agreement. Work had begun in 1991 to expand the GSM standard to the 1800 MHz frequency band and the first 1800 MHz network became operational in the UK in 1993. Also in 1993, Telecom Australia became the first network operator to deploy a GSM network outside of Europe and the first practical hand-held GSM mobile phone became available. In 1995, fax, data and SMS messaging services became commercially operational, the first 1900 MHz GSM network in the world became operational in the United States and GSM subscribers worldwide exceeded 10 million. In this same year, the GSM Association was formed. Pre-paid GSM SIM cards were launched in 1996 and worldwide GSM subscribers passed 100 million in 1998.

In 2000, the first commercial GPRS services were launched and the first GPRS compatible handsets became available for sale. In 2001 the first UMTS (W-CDMA) network was launched and worldwide GSM subscribers exceeded 500 million. In 2002 the first multimedia messaging services (MMS) were introduced and the first GSM network in the 800 MHz frequency band became operational. EDGE services first became operational in a network in 2003 and the number of worldwide GSM subscribers exceeded 1 billion in 2004.

By 2005, GSM networks accounted for more than 75% of the worldwide cellular network market, serving 1.5 billion subscribers. In 2005, the first HSDPA capable network also became operational.

9

The first HSUPA network was launched in 2007 and worldwide GSM subscribers exceeded two billion in 2008.

The GSM Association estimates that technologies defined in the GSM standard serve 80% of the

global mobile market, encompassing more than 5 billion people across more than 212 countries

and territories, making GSM the most ubiquitous of the many standards for cellular networks

INTRODUCTION

Global System for Mobile Communications (GSM)

WHAT IS GSM?

The Global System for Mobile communications is a digital cellular communications

system. It was developed in order to create a common European mobile telephone standard

but it has been rapidly accepted worldwide.

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Formerly it was Groupe Spéciale Mobile (founded 1982)

now: Global System for Mobile Communication

EVOLUTION OF GSM The idea of cell-based mobile radio systems appeared at Bell Laboratories (in USA) in the early

1970s. However, mobile cellular systems were not introduced for commercial use until the 1980s.

But in the beginnings of cellular systems, each country developed its own system, which was an

undesirable situation for the following reasons:  

The equipment was limited to operate only within the boundaries of each country.

The market for each mobile equipment was limited.

In order to overcome these problems, the Conference of European Posts and telecommunications (CEPT) formed, in 1982 ,the Group Special Mobile (GSM) in order to develop a pan-European mobile cellular radio system . The standardized system had to meet certain criteria:

Spectrum efficiency

International roaming

Low mobile and base stations costs

Good subjective voice quality

Compatibility with other systems such as ISDN (Integrated Services Digital Network)

Ability to support new services

GENERATION OF GSM 1st generation:- Analog mobile technologies :- AMPS , TACS & NMT.

2nd generation:- digital mobile technologies :- GSM , CDMA

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2.5generation:- Enhancement of GSM:- GPRS

3rd generation:- Technologies coursed by ITU-IMT

AMPS—Advanced Mobile Phone System

TACS----Total Access Communication System.

NMT----Nordic Mobile Telephones

Fig 1.1:-Generation of GSM

GPRS-Wireless Data Services .

EDGE—Provides 3 times the data capacity of GPRS.

3G---Uses WCDMA technologies Over Air interface (5MHz).

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GSM STANDARDSGSM-900 Standard

The GSM-900 standard is a standard for digital voice transmission in the 900 MHz band.

This so called “primary band" includes two sub bands of 25 MHz

GSM-1800 Standard

In GSM-1800, 1800 MHz band was allocated for digital mobile telephone services which

has frequency of 75 MHz. This was three times the bandwidth allocated for GSM-900.

GSM-1900 Standard

GSM-1900 is the standard for the 1900MHz band. It includes the same network

component as the GSM-900 or GSM-1800. The band width of this standard is 60 MHz.

GSM NETWORK

The GSM network can be divided into following broad parts.

The Mobile Station(MS)

The Base Station Subsystem (BSS)

The Network Switching Subsystem (NSS)

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The Operation Support Subsystem(OSS)

The Mobile Station (MS)

The mobile station (MS) consists of the mobile equipment (the terminal) and a smart card called the Subscriber Identity Module (SIM). The SIM provides personal mobility, so that the user can have access to subscribed services irrespective of a specific terminal. By inserting the SIM card into another GSM terminal, the user is able to receive calls at that terminal, make calls from that terminal, and receive other subscribed services. The mobile equipment is uniquely identified by the International Mobile Equipment Identity(IMEI). The SIM card contains the International Mobile Subscriber Identity (IMSI) used to identify the subscriber to the system, a secret key for authentication, and other information. The IMEI another IMSI are independent, thereby allowing personal mobility. The SIM card may be protected against unauthorized use by a password or personal identity number.

Functions of a Mobile Station :-

Radio transmission termination. Radio Channel Management.

Speech Encoding/Decoding .Radio Link error Protection.

Flow control of data. Mobility Management.

SIM (Subscriber identity Module) - It is basically a removable smart card in compliance with the ISO 7816 standard and a plug-in module (25 x 15 mm) .It includes a microprocessor with all the subscriber-related information . SIM (and consequently MS) is protected by a Personal Identification Number (PIN). It has a PIN Unblocking Key (PUK) used to unblock it.

Information stored in a SIM card- Serial number

International Mobile Subscriber Identity (IMSI)

Security authentication and cyphering information

Temporary Network information (LAI, TMSI)

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List of services subscribed by the user

The Base Station Subsystem (BSS)

The Base Station Subsystem (BSS) is composed of two parts, the Base Transceiver Station (BTS)

and the Base Station Controller (BSC).  These communicate across the specified Abis interface,

allowing (as in the rest of the system) operation between components made by different suppliers.

Fig 1.2:- The Base Station Subsystem Fig 1.3:- GSM BSS

The Base Transceiver Station (BTS) houses the radio tranceivers that define a cell and handles

the radiolink protocols with the Mobile Station.  In a large urban area, there will potentially be a

large number of BTSs deployed.  The requirements for a BTS are ruggedness, reliability,

portability, and minimum cost.

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The Base Station Controller (BSC) manages the radio resources for one or more BTSs.  It

handles radiochannel setup, frequency hopping, and handovers, as described below.  The BSC is

the connection between the mobile and the Mobile service Switching Center (MSC).  The BSC

also translates the 13 kbps voice channel used over the radio link to the standard 64 kbps channel

used by the Public Switched Telephone Network or ISDN.

Base Transceiver Station (BTS ):

The BTS houses the radio transceivers that define a cell and handles the radio link protocols

with the MS. In a large urban area, a large number of BTSs may be deployed.

Fig 1.4:- GSM BTS Fig 1.5:- A BTS Antenna in Paris

BTS is a network element with transmission and reception devices (transceivers) to and from

the MS, including

antennas

signal processing specific devices for the Air interface management

It can be considered as a complex radio modem controlled by the BSC

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It is involved also in the transmission and reception with the BSC through the A-bis interface

It has just executive functions (no management function)

Broadcast/receive to/from the MS either signalling and traffic signals

Perform source and channel coding

Modulate/Demodulate signals to be broadcasted/received through the Air interface radio channel

Multiplex the information to be transmitted over each carrier.

Transcoding and rate adaptation

Time and frequency synchronizing

INTERNAL VIEW OF BTS

Fig 1.6:- Internal View of BTS

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Fig 1.7:- 2-G BTS Fig 1.8:- 3-G BTS

The Base Station Controller (BSC):

The BSC manages the radio resources for one or more BTSs. It handles radio channel setup,

frequency hopping, and handovers. The BSC is the connection between the mobile and the MSC.

The BSC also translates the 13 Kbps voice channel used over the radio link to the standard 64

Kbps channel used by the Public Switched Telephone Network (PSDN) or ISDN.

It assigns and releases frequencies and time slots for the MS. The BSC also handles intercell

handover. It controls the power transmission of the BSS and MS in its area. The function of the

BSC is to allocate the necessary time slots between the BTS and the MSC. It is a switching device

that handles the radio resources.

BSC Functions:

Control of frequency hopping

Performing traffic concentration to reduce the number of lines from the MSC

Reallocation of frequencies among BTSs

Time and frequency synchronization

Power management

Time-delay measurements of received signals from the MS 18

Manage all the radio interfaces

Manage the handover procedures

Network Switching Subsystem (NSS)

Network switching subsystem (NSS) is the component of a GSM system that carries out

switching functions and manages the communications between mobile phones and the Public

Switched Telephone Network (PSTN). It is owned and deployed by mobile phone operators and

allows mobile phones to communicate with each other and telephones in the wider

telecommunications network. The architecture closely resembles a telephone exchange, but there

are additional functions which are needed because the phones are not fixed in one location. Each of

these functions handles different aspects of mobility management and is described in more detail

below.

The Network Switching Subsystem, also referred to as the GSM core network, usually refers to the

circuit-switched core network, used for traditional GSM services such as voice calls, SMS, and

circuit switched data calls.

The Home Location Register (HLR) and Visitor Location Register (VLR) , together with the

MSC, provide the call routing and (possibly international) roaming capabilities of GSM.  The HLR

contains all the administrative information of each subscriber registered in the corresponding GSM

network, along with the current location of the mobile.  The current location of the mobile is in the

form of a Mobile Station Roaming Number (MSRN) which is a regular ISDN number used to

route a call to the MSC where the mobile is currently located.  There is logically one HLR per

GSM network, although it may be implemented as a distributed database.

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Fig 1.9:- Network Switching Subsystem

The Visitor Location Register contains selected administrative information from the HLR,

necessary for call control and provision of the subscribed services, for each mobile currently

located in the geographical area controlled by the VLR.  Although each functional entity can be

implemented as an independent unit, most manufacturers of switching equipment implement one

VLR together with one MSC, so that the geographical area controlled by the MSC corresponds to

that controlled by the VLR, simplifying the signalling required.  Note that the MSC contains no

information about particular mobile stations - this information is stored in the location registers.

The other two registers are used for authentication and security purposes.  The Equipment

Identity Register (EIR) is a database that contains a list of all valid mobile equipment on the

network, where each mobile station is identified by its International Mobile Equipment Identity

(IMEI).  An IMEI is marked as invalid if it has been reported stolen or is not type approved.  The

Authentication Center is a protected database that stores a copy of the secret key stored in each

subscriber's SIM card, which is used for authentication and ciphering of the radio channel.

Home location register (HLR)

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The home location register (HLR) is a central database that contains details of each mobile phone

subscriber that is authorized to use the GSM core network. There can be several logical, and

physical, HLRs per public land mobile network (PLMN), though one international mobile

subscriber identity (IMSI)/MSISDN pair can be associated with only one logical HLR (which can

span several physical nodes) at a time.The HLR stores details of every SIM card issued by the

mobile phone operator. Each SIM has a unique identifier called an IMSI which is the primary key

to each HLR record.

The next important items of data associated with the SIM are the MSISDNs, which are the

telephone numbers used by mobile phones to make and receive calls. The primary MSISDN is the

number used for making and receiving voice calls and SMS, but it is possible for a SIM to have

other secondary MSISDNs associated with it for fax and data calls. Each MSISDN is also a

primary key to the HLR record. The HLR data is stored for as long as a subscriber remains with

the mobile phone operator.

Examples of other data stored in the HLR against an IMSI record is:

GSM services that the subscriber has requested or been given.

GPRS settings to allow the subscriber to access packet services.

Current location of subscriber (VLR and serving GPRS support node/SGSN).

Call divert settings applicable for each associated MSISDN.

Authentication centre (AUC)

The authentication centre (AUC) is a function to authenticate each SIM card that attempts to

connect to the GSM core network (typically when the phone is powered on). Once the

authentication is successful, the HLR is allowed to manage the SIM and services described above.

An encryption key is also generated that is subsequently used to encrypt all wireless

communications (voice, SMS, etc.) between the mobile phone and the GSM core network.

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If the authentication fails, then no services are possible from that particular combination of SIM

card and mobile phone operator attempted. There is an additional form of identification check

performed on the serial number of the mobile phone described in the EIR section below, but this is

not relevant to the AUC processing.

Proper implementation of security in and around the AUC is a key part of an operator's strategy to

avoid SIM cloning.

Visitor location register (VLR)

The visitor location register is a temporary database of the subscribers who have roamed into the

particular area which it serves. Each base station in the network is served by exactly one VLR,

hence a subscriber cannot be present in more than one VLR at a time.

The data stored in the VLR has either been received from the HLR, or collected from the MS. In

practice, for performance reasons, most vendors integrate the VLR directly to the V-MSC and,

where this is not done, the VLR is very tightly linked with the MSC via a proprietary interface.

Data stored include:

IMSI (the subscriber's identity number).

Authentication data.

MSISDN (the subscriber's phone number).

GSM services that the subscriber is allowed to access.

access point (GPRS) subscribed.

The HLR address of the subscriber.

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Equipment identity register (EIR)

The equipment identity register is often integrated to the HLR. The EIR keeps a list of mobile

phones (identified by their IMEI) which are to be banned from the network or monitored. This is

designed to allow tracking of stolen mobile phones. In theory all data about all stolen mobile

phones should be distributed to all EIRs in the world through a Central EIR. It is clear, however,

that there are some countries where this is not in operation. The EIR data does not have to change

in real time, which means that this function can be less distributed than the function of the HLR.

The EIR is a database that contains information about the identity of the mobile equipment that

prevents calls from stolen, unauthorized or defective mobile stations

Other support functions

Billing centre (BC)

The billing centre is responsible for processing the toll tickets generated by the VLRs and HLRs

and generating a bill for each subscriber. It is also responsible for to generate billing data of

roaming subscriber.

Short message service centre (SMSC)

The short message service centre supports the sending and reception of text messages.

Multimedia messaging service centre (MMSC)

The multimedia messaging service centre supports the sending of multimedia messages (e.g.,

images, audio, video and their combinations) to (or from) MMS-enabled Handsets.

Voicemail system (VMS)

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The voicemail system records and stores voicemails.

Network Management Subsystem

NMS is the third subsystem of GSM in addition to BSS and NSS. The purpose of NMS is to

monitor various functions and elements of the network. This system can often be referred to as

OSS as well.

The functions of NMS can be divided into three categories:

Fault Management

Configuration Management

Performance Management

These functions cover the whole of GSM network elements from the level of individual BTSs, up

to MSCs and HLRs.

Fault Management

Collection of alarm reports from network elements.

One point for managing all fault solutions.

The purpose of fault management is to ensure smooth operation of network and rapid

correction of any kind of problems detected. Fault management provides network operator with

information about the current status of alarm events and maintains a history database of alarms.

The alarms are stored in the NMS database and this database can be searched according to

criteria specified by the network operator.

Configuration Management

Management of radio network configuration.

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Maintain up to date information on the network element status.

The purpose of configuration management is to maintain up-to-date information about

operation and configuration status of network elements. Specific configuration functions

include management of radio network, software and hardware management of network

elements, time synchronization, and security operations.

Performance Management

Collection of measurement data from network elements.

Produce performance result from data.

In performance management, NMS collects measurement data from individual network

elements and stores it in a database. On the basis of the data, the network operator is able to

compare the actual performance of the network with planned performance and detect both

good and bad performance areas within the network.

Function of NSS :

Call control identification of the subscriber.

Establishing a call and release of the connection after the call is over.

Mobility management.

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Taking care of the location of the subscribers before, during and after a call.

Collecting the charging information about a call

Number of the caller and of the called subscriber

Length and type of the provided services

Transfer the acquired charging information to the Billing centre

Signalling with other networks and BSS through the different interfaces

Subscriber data handling

Data storage permanently or temporarily in some databases

OMCR:- It is used to monitor and maintain the alarms of the system.

GSM ARCHITECTURE

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Fig 2.0:- GSM Architechture

The added components of the GSM architecture include the functions of the databases and

messaging systems:

Home Location Register (HLR)

Visitor Location Register (VLR)

Equipment Identity Register (EIR)

Authentication Center (AuC)

SMS Serving Center (SMS SC)

Gateway MSC (GMSC)

Chargeback Center (CBC)

Transcoder and Adaptation Unit (TRAU)

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Different interfaces used in Mobile:

Um interface   The "air" or radio interface standard that is used for exchanges between a mobile (ME) and a base station (BTS / BSC).

Abis interface   This is a BSS internal interface linking the BSC and a BTS, and it has not been totally standardised. The Abis interface allows control of the radio equipment and radio frequency allocation in the BTS.

A interface   The A interface is used to provide communication between the BSS and the MSC. The interface carries information to enable the channels, timeslots and the like to be allocated to the mobile equipments being serviced by the BSSs. The messaging required within the network to enable handover etc to be undertaken is carried over the interface.

B interface   The B interface exists between the MSC and the VLR . As most VLRs are collocated with an MSC, this makes the interface purely an "internal" interface. The interface is used whenever the MSC needs access to data regarding a MS located in its area.

C interface   The C interface is located between the HLR and a GMSC or a SMS-G. When a call originates from outside the network, i.e. from the PSTN or another mobile network it ahs to pass through the gateway so that routing information required to complete the call may be gained. In addition to this, the MSC may optionally forward billing information to the HLR after the call is completed and cleared down.

D interface   The D interface is situated between the VLR and HLR.

E interface   The E interface provides communication between two MSCs. The E interface exchanges data related to handover between the anchor .

F interface   The F interface is used between an MSC and EIR. The communications along this interface are used to confirm the status of the IMEI of the ME gaining access to the network.

G interface   The G interface interconnects two VLRs of different MSCs and uses to transfer subscriber information, during e.g. a location update procedure.

H interface   The H interface exists between the MSC the SMS-G. It transfers short messages

I interface   The I interface can be found between the MSC and the ME. Messages exchanged over the I interface are relayed transparently through the BSS.

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SERVICES

Tele services

Bearer services

Supplementary

TELE SERVICES

It is the particular type of service which deals with voice communication and communication

which deals with Emergency calls via mobile communication.

It offers various services such as:-

Mobile telephony

Emergency calling

BEARER SERVICES

Include various data service for information transfer between GSM and other network like

P.S.T.N, I.S.D.N etc at the rate form 300 to 9600 bps. It also includes S.m.s (Short Message

Service). In which upto160 character alphanumeric data transmission to/from the mobile terminal

can be transmitted. It also includes various services such as U.M.S (Unified Messaging Services).

It also includes group 3 fax transmission. There also a technique provided by the GSM networks

such as Voice mailbox to save voice message. Also there is various techniques in latest handset to

use mailbox or to view mails anytime and anywhere using service known as electronic mail.

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SUPPLEMENTARY SERVICES

There are various services which are included in supplementary service such as:-

• Call Waiting- Notification of an incoming call while on the handset

• Call Hold- Put a caller on hold to take another call

• Call Barring- All calls, outgoing calls, or incoming calls

• Call Forwarding- Calls can be sent to various numbers defined by the user

• Multi Party Call Conferencing - Link multiple calls together

• CLIP – Caller line identification presentation

• CLIR – Caller line identification restriction

• CUG – Closed user group

CALL PROCESSINGThis section covers the procedures involved in establishing a call connection between subscribers

and the routing of the associated traffic.

An MS can participate in one of two types of calls :

Mobile Terminated Call : This is a call received by an MS that has been originated either from another MS (internal or external to the PLMN) or from a fixed network (e.g. PSTN) subscriber.

Mobile Originated Call : This is call originated by an MS within a PLMN.

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MS DIALS TO PSTN

1. MS acces the BTS for call through RACH.

2. BSS allots SDCCH to MS for signalling information.

3. BSS informs MSC the call request of MS.

4. MSC checks the subs. Authentification with VLR.

5. MSC request to GMSC to connect PSTN.

6. GMSC contacts the local exchange (LE)or called subs.

7. LE informs the availability of the called subs.

8. GMSC informs the same to MSC.

9. MSC asks the BSS to provide link to MS.

10. BSS allots the TCH to MS .

11. Call alert to both calling and called subs on FACCH.

12. Through connection made and billing starts.

Fig 2.1:- Call from Mobile to PSTN

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PSTN SUBSCRIBER DIALS TO MS

1. PSTN user dials the MSISDN, LE routes the call to GMSC.

2. GMSC uses the dialled MSISDN to determine the serving HLR asks the HLR to obtain MSRN.

3. The HLR requests the current serving VLR for MSRN to route to concerned MSC,VLR passes MSRN to HLR which is passed to GMSC,

4. GMSC routes the call to concerned MSC.

5. The MSC interrogates the VLR for current location area identity for MS

6. VLR provides LAI for MS.

7. MSC pages to MS via BSS;MS responds to the paging and set up the signalling link.

8. When the BSS eastablishes the necessary radio link the MSC is informed and the call is delivered to MS.

9. When the MS answers the call , the connection is completed to the calling PSTN number

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Fig 2.2:- Call from PSTN to Mobile

CALL CONNECTION

PROCEDURE

Fig 2.3:- Call connection procedure

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GSM HANDOVER

Mobile Stations within the cellular network are located in “cells”, these cells are provided by the

BSSs. Each BSS can provide one or more cells, dependent on the manufacturers’ equipment.

The cells are normally drawn as hexagonal, but in practice they are irregularly shaped, this is as a

result of the influence of the surrounding terrain, or of design by the network planners

Fig 2.4:- Cell Coverage of a Network

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When a subscriber moves from one cell to another during active call, the call is handed over to

another cell (neighbor cell), this process is called GSM Handover

HANDOVER , Who takes the decision….??

The handover decision is taken by BSC.

The actual execution of handover is responsibility of BSC and MSC.

The decision is based on the measurements results of the BTS and the MS.

Within the GSM system there are four types of handover that can be performed for GSM only

systems:

Intra-BTS handover:   This form of GSM handover occurs if it is required to change the frequency or slot being used by a mobile because of interference, or other reasons. In this form of GSM handover, the mobile remains attached to the same base station transceiver, but changes the channel or slot.

Inter-BTS Intra BSC handover:   This form of GSM handover or GSM handoff occurs when the mobile moves out of the coverage area of one BTS but into another controlled by the same BSC. In this instance the BSC is able to perform the handover and it assigns a new channel and slot to the mobile, before releasing the old BTS from communicating with the mobile.

Inter-BSC handover:   When the mobile moves out of the range of cells controlled by one BSC, a more involved form of handover has to be performed, handing over not only from one BTS to another but one BSC to another. For this the handover is controlled by the MSC.

Inter-MSC handover:   This form of handover occurs when changing between networks. The two MSCs involved negotiate to control the handover

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CONCLUSION

In the practical training for a period of 45 days, I have learned a lot about the present scenario in

the field of communication. I have gained knowledge about the technology used by the company –

GSM (GLOBAL SYSTEM FOR MOBILE COMMUNICATION).

GSM technology facilitates with high speed integrated data, voice data, fax, mail, voice mail and

mostly used SMS feature. GSM also make sure that all the communication made between

networks are secured and protected from intruders and frauds.

GSM actually brought the concept of being Mobile way beyond the limits. It enabled us to

communicate across the continents.

At our college we learn most of the things theoretically, which does not provides sufficient

information about the subject, and students remain unaware of the problems and errors when they

go to the field. This practical training has provided us the knowledge about various technologies in

the communication field.

I am highly grateful to the ITTM (A unit of MTNL DELHI). for the support and guidance given

to us for the successful completion of our practical training.

The future of telecom is undeniably bright, with the development of new software, and

increasingly sophisticated hardware and new telecomm operators such as Idea, Airtel, Vodafone,

Aircell etc.

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Telecomm side is one of the best sides where a student can search for his future in the upcoming

time as definitely telecomm side demands for various new engineers with their best potentials.

REFERENCES

1. www.google.com

2. www.mtnldelhi.in

3. www.123eng.com

4. www.wikipedia.com

5. www.docstoc.com

6. www.gsmworld.com

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